1. Field of the Invention
The present invention relates to a sheet discharge unit for discharging sheets of paper or the like or a sheet supply unit for supplying sheets, and particularly relates to the improvement of a sheet discharge unit, a sheet supply unit and sheet processing apparatus using these units, which improvement being effective in discharging or supplying long sheets.
2. Description of the Related Art
An example of a sheet processing apparatus is an image forming apparatus using an electro-photographic system or the like.
In such image forming apparatus in the related art, an imaging engine using an electro-photographic system or the like is mounted in an apparatus body so that the imaging engine forms an image. On the other hand, a sheet of paper or the like is supplied from a sheet supply unit to the imaging engine, and the image formed by the imaging engine is transferred and fixed to the sheet. Then, the sheet is discharged to a sheet discharge unit.
In such image forming apparatus, there is a request to use long sheets. To satisfy the request, for example, there is adopted a system in which long sheets are set in a manual sheet insertion type sheet supply unit, and discharged to a discharge tray as a sheet discharge unit after an imaging cycle is performed on the long sheets.
There has been proposed a manual sheet insertion type sheet supply unit in which one stage of an assistant tray or plural stages of assistant trays are provided movably at the rear edge of a manual sheet insertion tray, and a sheet loading surface which can be loaded with long sheets including their rear ends is secured by the manual sheet insertion tray and the assistant tray(s), so that the manual sheet insertion type sheet supply unit can be extended for exclusive use of the long sheets. Such type of sheet supply unit is disclosed in JP-A-2001-163454 (at Mode for Carrying Out the Invention and FIG. 1) and in JP-UM-A-3-28145 (at Example of embodiment and FIG. 1).
However, the length of the discharge tray as a sheet discharge unit is generally fitted to the length of a largest form sheet. Therefore, when a long sheet is discharged, there may occur a problem that a part of the long sheet protrudes from the discharge tray and falls therefrom, or the falling long sheet curls up.
Therefore, of such image forming apparatus, there has been proposed apparatus by which long sheets can be supplied and discharged without increasing the apparatus area.
According to this proposal, there is disclosed in JP-A-6-179529 (at Example of embodiment and FIG. 1) that the image forming apparatus is mounted on a paper supply/discharge unit, and long sheets to be supplied are received in a space secured between the image forming apparatus and the paper supply/discharge unit, while the discharged paper is received on a table for mounting the paper supply/discharge unit thereon.
However, in such image forming apparatus, the sheet reception space for supplying or discharging the long sheets has to be not smaller than the regular running sheet size. Thus, in the related art, it is essential to provide both the space for supplying the long sheets and the space for discharging the long sheets. As a result, the area for installing the image forming apparatus is not increased so much, but a large volume is required for the space for receiving the long sheets.
In addition, a technique in which a lid or a cover of a sheet supply cassette is designed to be drawable so that the drawn lid or the drawn cover is used as a discharge tray of a sheet discharge unit has been proposed in JP-A-8-026502 (at Example of embodiment and FIG. 1) and in JP-A-9-002673 (at Example of embodiment and FIG. 1).
However, the lid or the cover becomes essential for the sheet supply cassette to load discharged sheets thereon so that the cost of parts increases correspondingly. In addition, since the lid or the cover having a function as a discharge tray is drawn from the sheet supply cassette, the length of the discharge tray is restricted to the length of the sheet supply cassette.
Accordingly, sheets to be used have to be received in at least the sheet supply cassette. However, when it is intended to support long sheets of various sizes, it is inevitable to increase the length of the sheet supply cassette. It is therefore difficult to receive the sheet supply cassette in the image forming apparatus body.
Thus, when long sheets are used while the sheet supply cassette is received in the image forming apparatus body, setting of the long sheets in the sheet supply cassette is regarded as difficult so that the current situation almost seems to be that there is no choice but to use a manual sheet insertion tray for setting the long sheets.
Further, in a manual sheet insertion type sheet supply unit supporting long sheets, an assistant tray is added to a manual sheet insertion tray. However, the image forming apparatus itself has no way to judge whether the assistant tray has been added to the manual sheet insertion tray or not. The judgment has to totally depend on a user.
As a result, the following technical problem can be found. That is, for example, when long sheets are intended to be supplied from the manual sheet insertion tray though the assistant tray has not been added, the image forming apparatus executes an imaging process as it is. Thus, an image defect is caused by a failure in transport such as skew of a long sheet.